GSA Connects 2021 in Portland, Oregon

Paper No. 102-4
Presentation Time: 2:20 PM


BRANDL, Collin, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87196, WORTHINGTON, Lindsay Lowe, Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131, MAGNANI, Maria Beatrice, Roy Huffington Department of Earth Sciences, Southern Methodist University, 3225 Daniel Ave, Dallas, TX 75205-1437, SHILLINGTON, Donna J., School of Earth and Sustainability, Northern Arizona University, 625 S. Knoles, Flagstaff, AZ 86011 and LUCKIE, Thomas, Earth Sciences, University of Southern California, 3651 Trousdale Pkwy, Los Angeles, CA 90089-0740

We used wide-angle marine active source seismic data from the 2014-2015 GeoPRISMS Eastern North American Margin (ENAM) Community Seismic Experiment (CSE) to investigate along-strike changes in igneous addition beneath the East Coast Magnetic Anomaly (ECMA). The ENAM formed during the breakup of Pangea ~200 myr ago and its crustal structure records extension and magmatism during rifting, as well as the rift to drift transition. Here, previous strike-perpendicular imaging showed igneous addition to the margin as seaward dipping reflectors and high velocity lower crust (HVLC) but along-strike variability implied by potential field anomalies could not be constrained without high resolution along-strike imaging. Constraints on along-strike crustal structure of the ENAM can provide insight into small scale processes that may be critical for a successful rift to drift transition and that influence later mid ocean ridge segmentation.

Tomographic modeling from ocean bottom seismometer data on lines 4A and 4B of the ENAM CSE shows a P-wave velocity structure resembling extremely thick oceanic-type crust. We observe minimal along-strike variations in crustal thickness, but substantial variations in the extent of HVLC. Within the HVLC sections, velocities at the base of the crust reach ~7.5 km/s, while two ~30 km-wide gaps are present where velocities only reach ~7.0 km/s. The gaps in HVLC align with isostatic gravity lows and with extrapolated Mid-Atlantic Ridge fracture zones. Mantle melting models indicate that the >7.5 km/s HVLC most likely represents heavy igneous intrusion into extended continental crust while the HVLC gaps most likely represent nearly unaltered extended continental crust. The along-strike intrusion variability also affects the volume of igneous addition, reducing it by up to 76% from previous whole margin estimates. Our along-strike observations closely match fracture zone formation modeling from the less magmatic Woodlark Basin where magmatic centers undergo the rift to drift transition and then connect into a stable ridge configuration. It is unclear what influenced segmentation of the Pangean rift, but it appears that the segmentation of the early rift resulted in a lower volume of igneous addition and directly influenced Mid-Atlantic Ridge segmentation.